This invention relates to a solid state, microcontroller controller for controlling operation of a grain dryer. The controller of the present invention may be used with a variety of grain dryers, but the controller of the present invention will herein be described in conjunction with a vertical flow grain dryer that may be operated in continuous batch, staged automatic, or continuous flow drying modes.
Typically, such a grain dryer comprises a housing having an outer basket of perforate construction and an inner basket also of perforate construction with the inner basket spaced from the outer basket a desired distance (e.g., fourteen inches) so as to form a column of grain to be dried. The wet grain to be dried is delivered to a horizontal garner bin at the top of the dryer. Both the inner and outer baskets are usually concentric relative to one another and are in the form of a vertically disposed diamond shape (when viewed in cross section) such that wet grain from the garner bin is split into two columns, one on each side of the inner basket, by the upper pointed end of the inner basket such that substantially equal quantities of grain flow down the path defined by the grain columns on each side of the inner basket. One or more fans/heater units at one end of the dryer forces heated air into the interior of the inner basket such that the inner basket constitutes a drying or plenum chamber. The heated air is distributed in the plenum chamber and is forced through the perforate inner basket into the grain column to dry the grain in the grain column. The air with the moisture from the grain is discharged to the atmosphere as it passes through the perforate outer basket.
The wet grain is loaded into a garner bin at the top of the dryer by a loading auger or the like. A horizontal auger in the garner bin distributes the grain horizontally such that there is a uniform quantity of grain in the garner bin from one end of the dryer to the other. After the grain has traveled downwardly through the grain column and after it has been dried, the dried grain is discharged from the bottom of the grain column. At the bottom of the grain column, metering rolls are provided which are positively driven so as to control the rate at which dried grain is conveyed from the grain column. The dried grain is discharged into a horizontal grain discharge conduit. The rate of operation of the metering rolls controls the rate of movement of the grain through the dryer and thus regulates the throughput of the dryer. A discharge auger is located in the discharge conduit so as to convey the dried grain from the dryer. The dried grain discharged from the dryer is oftentimes deposited in a pickup well from which it is conveyed to a holding or conditioning bin by way of another auger conveyor.
The fan/heater assembly typically includes an axial flow fan which forcefully draws large quantities of air into a relatively large cylindrical housing and forces the air through the housing and into the drying chamber. (Although the fan is preferably an axial flow fan, centrifugal fans or other types may also be used. Similarly, although a cylindrical housing is primarily used, other housing shapes such as rectangular or square may also be used.) The heater is usually a gas fired burner fueled by liquid propane or the like. The burner is located within the cylindrical housing downstream from the fan such that the fuel is burned within the housing and such that the flame and the products of combustion mix with the air flowing through the housing thereby to heat the air to a desired temperature. In certain models of dryers, only a single fan/heater unit is used. In other dryers, two or three fan/heater units, one on top of the other, are employed. In modular stack dryers, two or even three grain dryers (which need not all be identical) such as above described are stacked vertically one on the other with the grain from the uppermost dryer flowing directly into the grain columns of the next lower dryer with the different dryers being programmed to dry the grain in stages. In fact, because of the ability of the present control system to control different models and sizes of dryers using the same control circuitry, the dryers in a stack can be of very different construction, size, etc. and still be controlled by a single control circuit.
A controller for such a dryer must control operation of the inlet and outlet augers supplying wet grain to the dryer and carrying away dried grain. The controller must also control the operation of the fan/heater units, the upper and lower grain augers, and the metering rolls. The controller must monitor a number of temperature sensors located in various locations within the dryer so as to enable automatic operation of the dryer to dry the grain to a desired moisture level without overheating the grain (which could cause damage to the grain), and must shut down operation of the dryer in the event certain parameters being monitored by the controller are outside limits established for these parameters corresponding to undesirable operating conditions for the dryer.
Prior art dryer controllers typically were analog electromechanical systems. These prior art controllers were difficult and expensive to manufacture, were difficult to reconfigure or change to accommodate different grain drying conditions, which oftentimes required that components (e.g., timers) be physically replaced to change dryer control parameters. Further, the reliability of such electromechanical systems was not at the level that was desired.
Prior art dryer controllers had several shortcomings. For example, in the event a prior art dryer controller would sense a dryer shutdown condition and would shut down the dryer, the controller typically would have a series of indicator lights that would help locate the source of the shutdown. However, in the event of a shutdown, many operators would immediately attempt to re-start the dryer. This re-start procedure would re-set all of the indicator lights so that the operator would not know the likely source of the shutdown (unless the operator either remembered or wrote down the indicator light that was lit) in the event the dryer needed to be serviced.
Prior art controllers would allow all of the motors on the dryer to start simultaneously thus resulting in current draws that may exceed the capability of the electric service available for the dryer. In many dryer installations of a farm or the like, the available electric service may only be 230 volts, single phase power. With prior art controllers, it was necessary for the operator to manually startup the dryer in such manner that only one motor was started at a time to insure that the current draw for the dryer was maintained within the capability of the electric service available. Many operators would not follow proper startup procedures.
Also, prior art controllers could not differentiate between safety related shutdown conditions (e.g., a grain over temperature or detection of a flame) and a non-critical shutdown condition (e.g., an out of incoming grain condition). Difficulty would oftentimes be experienced in that shutdown of the unloading auger would result in the auger becoming jammed, thus requiring a time consuming manual unloading of the dryer or the unloading auger. This necessitated considerable additional work and time required to get the dryer back in operation after a non-critical shutdown.
It will also be appreciated that a manufacturer offering a full line of dryers so as to serve small on-farm drying requirements and large commercial grain storage facilities, a large number of dryer models are necessary. For example, Grain Systems, Inc. of Assumption, Ill. offers about sixty-two (62) models of the above-described grain dryers. With prior art electromechanical controllers, it was necessary to have a different controller for every different dryer model. This presented logistical problems in manufacturing the dryers and also present difficulties in servicing the dryers in the field and in stocking replacement controllers for these dryers.